Examples of high-efficiency and low-current-loss electric apparatuses capable of solving recent problems in energy, the environment, and resources include superconducting apparatuses such as a cable, a coil, a motor, and a magnet in which a superconductor is used as a low-current-loss material. As a superconductor used in these superconducting apparatuses, for example, an oxide superconductor such as a RE-123-based oxide superconductor (REBa2Cu3O(7-x): RE represents a rare-earth element such as Y or Gd) is known. This oxide superconductor exhibits superconducting characteristics at about a liquid nitrogen temperature and can maintain a relatively high critical current density even in a ferromagnetic field. Therefore, it is considered that the oxide superconductor can be applied to a wider range as compared to other superconductors, and the oxide superconductor is expected to be a practically promising material.
In order for the oxide superconductor to be used in an electric apparatus, in general, the oxide superconductor is processed into a wire to be used as an oxide superconducting wire such as a power supply conductor or a magnetic coil. The oxide superconducting wire is formed by forming an oxide superconducting layer on a tape-shaped substrate with an interlayer interposed therebetween.
It is known that, when the oxide superconductor is placed in a high-humidity environment, a crystal structure thereof is disordered due to an influence of moisture, and superconducting characteristics decrease. Therefore, it is necessary to protect the oxide superconducting layer from moisture. To that end, a technique of protecting the oxide superconducting layer from moisture by forming an undercoat stabilizing layer containing Ag thereon is known.
Ag is a relatively expensive metal, and thus less Ag used, the better. Therefore, the undercoat stabilizing layer containing Ag formed is thin. However, when the undercoat stabilizing layer of Ag is thin, satisfactory moisture resistance may not be obtained, and thus various structures are provided.
For example, a structure is known, in which an oxide superconducting layer is formed on a substrate with an interlayer interposed therebetween to obtain a laminate, an undercoat stabilizing layer is formed on the oxide superconducting layer of the laminate, and a stabilizing layer of Cu or the like is formed on an outer periphery of the laminate including the undercoat stabilizing layer using an electroplating method to liquid-tightly seal the outer periphery of the oxide superconducting wire.
However, the current densities flowing through the respective layers constituting the oxide superconducting wire are not the same because they depend on the respective electrical resistances thereof. Accordingly, there is a problem in that the thickness of the stabilizing layer is not uniform. In addition, a Ni-based alloy (for example, HASTELLOY: trade name, manufactured by Haynes International, Inc.), which is known to be preferable as a material of a substrate, is known as a material on which it is difficult to form a plating layer. Even when a Cu plating layer is formed on a Ni-based alloy, the Cu plating layer (stabilizing layer) may be peeled off due to poor adhesion.
Therefore, PTL 1 discloses a technique of forming a stabilizing layer having a uniform thickness by completely covering an outer periphery of a laminate with an undercoat stabilizing layer containing Ag, and providing a Cu stabilizing layer on the undercoat stabilizing layer using a plating method, the laminate including: a substrate; and an oxide superconducting layer that is formed on the substrate with an interlayer interposed therebetween.